As is well known in the art, hot runner injection molding systems include a manifold for conveying pressurized melt from an inlet to one or more manifold outlets. An injection molding apparatus may also include a nozzle having two nozzle bodies. An example of an injection molding apparatus having two nozzle bodies in tandem can be found in U.S. Pat. No. 4,818,217 to Schmidt et al., which is incorporated herein by reference in its entirety. In particular, these nozzles are used in situations where it is desirable to have a longer nozzle than a conventional nozzle, or an extended nozzle. For example, an extended nozzle may be used when the injection of the plastic and the ejection of the product are mounted on the same side of the mold. Another environment where extended nozzles may be useful is when multiple split molds are used with a single hot runner manifold. This type of apparatus is generally described in U.S. Pat. No. 3,843,295 to Greenberg et al., which is incorporated herein by reference in its entirety.
Thermal expansion can cause tandem nozzles to expand, causing a downstream nozzle to push against an adjacent mold plate. One solution to this problem is to have one nozzle telescope inside another to form a sliding interface between the two nozzles. Thus, as the nozzles thermally expand, the interface between the nozzles can adapt to account for the thermal expansion. However, such an interface between the nozzles can cause leakage, particularly when thermal expansion causes shifting between the two nozzles.
Further, melt flowing through a nozzle channel provides best results when maintained at a consistent temperature. Thus, a heater is generally provided for a nozzle along its length to control the temperature of the melt.